The present invention relates to liquid crystal display apparatuses.
In the liquid crystal display apparatus, a cold cathode tube has hitherto been used as a backlight source but recently, a module having a semiconductor light emitting diode (LED) element applied to the backlight source has been developed for liquid crystal televisions. In a compact liquid crystal panel for use in a cell phone, a white light source having a blue semiconductor light emitting diode element and a yellow fluorescent substance in combination has been used for backlight. But for medium and large size liquid crystal display panels, an LED backlight module is needed in which LED elements for three primary colors of red, green and blue are built in and they are controlled independently to improve the color display performance with high picture quality.
In constituting the backlight module, it is important that the LED element to be mounted is highly efficient in order to reduce consumptive power as far as possible. The LED element mounted on the backlight is structured more advantageously in the flip chip mounting form characteristic of a wide divergence having the ability to take out a large quantity of light from a transparent substrate than in the bonding mounting form using a gold wire. The flip-chip element can optically have emission efficiency nearly twice that of the wire bonding element but electrically, it faces a problem that the current density distribution in the element is localized or biased to make the emission intensity distribution non-uniform. For this reason, an improvement needs to be made to provide uniform emission intensities in different directions and attain an intended high brightness.
In the wire bonding mounting, too, an improvement must be made to attain an electrically uniform current density distribution and there needs a countermeasure including a structural form and a light take-out structure with a view to improving the emission efficiency.
In known prior arts trying to cope with these problems, the shape of electrode is contrived and besides a current diffusion layer is applied in order that the current distribution in the light emitting diode element can be uniform as indicated in JP-A-2004-363572 by Toshiki Yoshiuji et al and JP-A-2002-151739 by Ryouichi Takeuchi et al. In JP-A-5-13816 by Masaki Mori et al, a trail is made to provide an insulating film between electrodes for the sake of avoiding electrical short-circuit between the electrodes and realizing steady mounting with a high yield in the course of mounting a flip-chip element. In JP-A-10-107316 by Masayoshi Koike et al, a method is described according to which a plurality of electrically separated operating regions are formed in a single LED element integrally therewith and individual regions are electrically connected by a surface electrode pattern to reduce steps in die bonding and wire bonding, thus reducing costs. In JP-A-2004-235441 by Seishi Tamura et al and JP-A-2004-207655 by Tatsumi Setomoto et al, methods are described in which with a view to mounting an LED element to a wiring substrate with high accuracy, a wiring pattern is contrived and an alignment mark shape is so contrived as to be introduced to a substrate.